Complimenting modern records of tropical cyclone activity with longer historical and paleoclimatological
records would increase our understanding of natural tropical cyclone variability on decadal to centennial time
scales. Tropical cyclones produce large amounts of precipitation with significantly lower δ18O values than
normal precipitation, and hence may be geochemically identifiable as negative δ18O anomalies in marine
carbonate δ18O records. This study investigates the usefulness of coral skeletal δ18O as a means of
reconstructing past tropical cyclone events. Isotopic modeling of rainfall mixing with seawater shows that
detecting an isotopic signal from a tropical cyclone in a coral requires a salinity of ~33 psu at the time of coral
growth, but this threshold is dependent on the isotopic composition of both fresh and saline end-members. A
comparison between coral δ18O and historical records of tropical cyclone activity, river discharge, and
precipitation from multiple sites in Puerto Rico shows that tropical cyclones are not distinguishable in the
coral record from normal rainfall using this approach at these sites.

Tropical small mountainous rivers deliver a
poorly quantified, but potentially significant, amount of
carbon to the world’s oceans. However, few historical
records of land–ocean carbon transfer exist for any region
on Earth. Corals have the potential to provide such records,
because they draw on dissolved inorganic carbon (DIC) for
calcification. In temperate systems, the stable- (d13C) and
radiocarbon (D14C) isotopes of coastal DIC are influenced
by the d13C and D14C of the DIC transported from adjacent
rivers. A similar pattern should exist in tropical coastal
DIC and hence coral skeletons. Here, d13C and D14C
measurements were made in a 56-year-old Montastraea
faveolata coral growing *1 km from the mouth of the Rio
Fajardo in eastern Puerto Rico. Additionally, the d13C and
D14C values of the DIC of the Rio Fajardo and its adjacent
coastal waters were measured during two wet and dry
seasons. Three major findings were observed: (1) synchronous
depletions of both d13C and D14C in the coral
skeleton are annually coherent with the timing of peak river
discharge, (2) riverine DIC was always more depleted in
d13C and D14C than seawater DIC, and (3) the correlation
of d13C and D14C was the same in both coral skeleton and
the DIC of the river and coastal waters. These results
indicate that coral skeletal d13C and D14C are recording the
delivery of riverine DIC to the coastal ocean. Thus, coral
records could be used to develop proxies of historical land–
ocean carbon flux for many tropical regions. Such information
could be invaluable for understanding the role of
tropical land–ocean carbon flux in the context of land-use
change and global climate change.

Tropical small mountainous rivers (SMRs) may transport up to 33% of the total
carbon (C) delivered to the oceans. However, these fluxes are poorly quantified and
historical records of land-ocean carbon delivery are rare. Corals have the potential to
provide such records in the tropics because they are long-lived, draw on dissolved
inorganic carbon (DIC) for calcification, and isotopic variations within their skeletons are
useful proxies of palaeoceanographic variability. The ability to quantify riverine C inputs
to the coastal ocean and understand how they have changed through time is critical to
understanding global carbon budgets in the context of modern climate change. A seasonal
dual isotope (13C & 14C) characterization of the three major C pools in two SMRs and
their adjacent coastal waters within Puerto Rico was conducted in order to understand the
isotope signature of DIC being delivered to the coastal oceans. Additionally a 56-year
record of paired coral skeletal C isotopes (δ13C & Δ14C) and trace elements (Ba/Ca,
Mn/Ca, Y/Ca) is presented from a coral growing ~1 km from the mouth of an SMR. Four
major findings were observed: 1) Riverine DIC was more depleted in δ13C and Δ14C than
seawater DIC, 2) the correlation of δ13C and Δ14C was the same in both coral skeleton
and the DIC of the river and coastal waters, 3) Coral δ13C and Ba/Ca were annually
coherent with river discharge, and 4) increases in coral Ba/Ca were synchronous with the
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timing of depletions of both δ13C and Δ14C in the coral skeleton and increases in river
discharge. This study represents a first-order comprehensive C isotope analysis of major
C pools being transported to the coastal ocean via tropical SMRs. The strong coherence
between river discharge and coral δ13C and Ba/Ca, and the concurrent timing of increases
in Ba/Ca with decreases in δ13C and Δ14C suggest that river discharge is simultaneously
recorded by multiple geochemical records. Based on these findings, the development of
coral-based proxies for the history of land-ocean carbon flux would be invaluable to
understanding the role of tropical land-ocean carbon fluxes in the context of global
climate change.